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Orion Nebula binary star resolved by VLTI

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 02 April, 2009

Using ESO’s Very Large telescope Interferometer (VLTI), astronomers have plunged into the heart of the Orion Trapezium Cluster to produce the sharpest image ever obtained of the young double star Theta 1 Ori C.

Zooming in on the four bright Trapezium stars (Theta 1 Ori A-D), the dominant star is Theta 1 Ori C. Right: The orbit of the binary system (grey line) was derived using position measurements obtained over the last 12 years (yellow points). Image: MPIfR (Stefan Kraus), combining the VLTI image of Theta 1 Ori C with images from VLT/ISAAC (ESO) and HST (NASA, Chris O'Dell).

With a spatial resolution of about two milli-arcseconds, the new image clearly separates the two young, massive stars in this intense nearby star-forming region. Furthermore, the team of astronomers working on the project, led by Stefan Kraus and Gerd Weigelt from the Max-Planck-Institute for Radio Astronomy (MPIfR) in Bonn, was able to derive key properties of the binary system.

Measurements taken over the last 12 years show that the two stars are on a very eccentric orbit with a period of 11 years. They also established that the masses of the two stars were 38 and 9 solar masses and that they lie 1,350 light years away from Earth. The results are important for studies of the Orion region as well as the improvement of theoretical models of high-mass star formation.

These accurate measurements would not have been possible without the high resolution stellar imaging achievable with the VLTI/AMBER instrument. Interferometry allows astronomers to combine the light from several telescopes, forming a huge virtual telescope with a resolving power corresponding to that of a single telescope of tens or even hundreds of metres in diameter.

ESO's 8.2m-UT (big domes) and 1.8m-AT telescopes (small domes in the foreground) on Cerro Paranal. A virtual telescope of 130 m diameter, formed by combining the light from three AT's arranged in three different telescope configurations, was used to construct the image of Theta 1 Ori C. Image: MPIfR (Gerd Weigelt).

“Our observations demonstrate the fascinating new imaging capabilities of the VLTI,” says Weigelt. “This infrared interferometry technique will certainly lead to many fundamental new discoveries.”

Theta 1 Ori C originally appeared to be a single star in previous images derived from both conventional telescopes and the Hubble Space Telescope. It is the most luminous star in the Orion Nebula, and its intense radiation is ionizing the whole region, with its strong winds shaping the famous Orion proplyds, young stars still surrounded by their protoplanetary dust discs.

A paper discussing the results appears in the journal Astronomy and Astrophysics.

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